1. Field of the Invention
The present invention relates to a numeric control unit for a turning mechanism which turns a turning body around a designated turning shaft through a non-linear transmitting mechanism by a driving source moving in a non-circular movement.
2. Description of the Related Art
Conventionally, in a machine tool or the like which is provided with a turning mechanism which turns a turning body around a designated turning shaft, a turning mechanism which has a driving source to move in a linear motion, and a transmitting mechanism which transmits the linear motion by the driving source to the turning body. As for a transmitting mechanism, a rack and pinion mechanism, a worm-gear mechanism and so on are used.
Among such turning mechanisms, there is a turning mechanism which turns a turning body using a cam mechanism, for instance, a turning mechanism shown in Japanese Patent Application No. Hei 8-198035.
This turning mechanism 1 is formed, as shown in FIG. 12, including a turning bodies 12 supported by a base member 11 as possible to turn, a driving source 13 which turns the turning body 12 and a transmitting mechanism 14 which transmits the movement of the driving source 13 to the turning body 12.
The turning body 12 is supported by a supporting shaft 15 as possible to turn around a turning shaft A to a base member 11, and on the tip thereof, a concave portion 121 is formed to engage in a connecting shaft 143 which will be explained later.
A main shaft head 122 in a built-in motor system is provided near the turning shaft A of the turning body 12, and it becomes possible that the main shaft head 122 turns in accordance with the turning movement of the turning body 12 to perform various processing on a work piece.
The driving source 13 is provided with: a servo-motor 131; a pinion gear 132 which meshes with a gear wheel provided on the tip of the revolving shaft of the servo-motor 131; a feed screw rod 133 rotated by the pinion 132 in accordance with the revolution of the revolving shaft of the servo-motor 131; and a feed nut 134 which screws with the feed screw rod 133, and moves in a linear movement along the extending direction of the feed screw rod 133.
A transmitting mechanism 14 which transmits a linear movement of the feed nut 134 of the driving source 13 to the turning body 12 is comprised with a horizontal slider 141, a vertical slider 142, and a connecting shaft 143.
The horizontal slider 141 is attached in a movable manner in the extending direction of the horizontal guide 111 which is linearly mounted on the base member 11, and a vertical guide 141A perpendicularly extending into the extending direction of the horizontal guide 111 is constructed on the upper surface of the slider 141.
The vertical slider 142 is attached in a movable manner in the direction of the vertical guide 141A and the connecting shaft 143 which engages with the concave portion 121 of the turning shaft 12, is provided on the upper surface of the vertical slider 142.
The feed nut 134 of the driving source 13 is jointly fixed to the horizontal slider 141 on the right.
The horizontal sliders 141 provided on the two turning bodies 12 respectively, are connected to each other by a connecting rod 144, and according to the turning movement of the turning body 12 shown in the right side on FIG. 12, the other turning body 12 also turns.
The turning mechanism 1 behaves as follows.
1) When the servo-motor turns, the feed screw rod 133 rotates through the pinion gear 132. PA1 2) The feed nut 134 moves along the direction extending from the feed screw rod 133 by the rotation of the feed screw rod 133. PA1 3) In accordance with the movement of the feed nut 134, the horizontal slider 141 moves and the turning body 12 turns through the connecting shaft 143. PA1 X: position of the linear driving of the driving source. PA1 .theta.: the turn angles of the turning body PA1 t: time PA1 X=f (.theta.), X and .theta. are all functions of t.
While the horizontal slider 141 is moving, the connecting shaft 143 moves with the vertical slider 142 along the vertical guide 141A to maintain engagement with the concave portion 121 of the turning body 12.
As shown in FIG. 13, a path 143A of the connecting shaft 143 form an arc in .theta. direction around the turning shaft A to a path 134A of the feed nut 134 in the X direction.
According to the turning mechanism 1, a linear movement of the driving source 13 can be transmitted to the turning movement of the turning body 12 through a simple motion along the guides 111 and 141A of the horizontal slider 141 and the vertical slider 142.
Therefore, a turning mechanism having an extreme durability can be formed with no fear of a turning motion failure caused by the abrasion of the mesh portion as in the case of a rack and pinion mechanism or a worm gear mechanism.
When plural turning bodies 12 in a rack and pinion transmitting mechanism and the like are placed adjacent to each other, it is necessary to take a large space interval for each element so that the gear of the adjacent transmitting mechanism does not interfere with each other. On the other hand, when the turning mechanism 1 described above is used, there is no need to take it into consideration, and the turning bodies 12 can be placed near to each other, so that a machine tool having plural turning bodies can be made small size.
In order to machine a work piece with high precision with the turning mechanism 1 in a machine tool and the like, it is necessary to enhance the positioning precision of the turning body to the inputted turn angle signal, and stabilize the turn velocity of the turning body with high precision. Particularly, in a multi-shaft high precision machine tool for contour processing such as a profiler and the like, achievement of a high precision in positioning and turn velocity is an important subject.
However, as shown in FIG. 13, since such a turning mechanism 1 converts a linear movement of the feed nut 134 into a turn movement of the turning body 12, the distance between the turning shaft A and a driving point of the straight line (the position of the feed nut 134) of the driving source 13 varies in accordance with the turn angles .theta.. This means that even when the feed nut 134 moves with constant velocity along the path 134A, the turn velocity of the turning body 12 varies.
Therefore, in order to turn the turning body 12 while maintaining constant turn velocity, the linear movement of the driving source 13 must be controlled to change in response to the turn angles .theta..
More specifically, since the linear movement of the driving source 13 is converted to the turning movement of the turning body 12, the driving source 13 must be driven with trigonometric-functionally changing the movement velocity of the driving source 13.
When a positional error (droop) Ex arises at the driving point of the straight line of the driving source 13, a positional error E.sub..theta. of the turning body which follows the linear movement varies in accordance with the turn angles.
Accordingly, the positional error E .sub..theta. must be controlled in response to the angles .theta. to be the same as in the case of direct driving through the revolution driving source.
Such a subject is grasped not only in the turning mechanism 1 which transmits the movement of the driving source 13 to the turning body through the transmitting mechanism 14, but also in the turning mechanism which applies a non-linear transmitting mechanism such as a link mechanism and the like.
In a numerical control device of a turning mechanism which turns a turning body with a non-circularly-moving driving source through a non-linear transmitting mechanism, it is an object of the present invention to provide a numerical control device of a turning mechanism which enables it to stabilize the turn velocity of the turning body with a high precision and to control the droop of the driving source in a similar manner to the case when driven with a revolution driving source.